The present invention relates to pistons for engines or motors, for example, internal combustion engines, or hydraulic or pneumatic reciprocating motors. In particular, the invention relates to pistons comprising a crown and a skirt.
The present invention is concerned with the construction of the piston skirt, or to part of a skirt having at least one insert therein, the insert being of a different material from that of the remainder of the piston skirt.
It is known to reduce the weight of a piston by replacing a metal skirt with a skirt of a plastics material secured within the piston.
It is known to provide plastic inserts for several different purposes. Thus, for example, in UK patent specification No. 2,162,614 it is disclosed to provide on each of both thrust faces of a piston skirt a plurality of plastic inserts to transmit lateral thrusts of the piston against a cylinder wall. Further, in order to reduce wear of the plastic inserts it is disclosed that each plastic insert is bevelled appropriately to cause provided lubrication to be forced over the plastic inserts by a hydrodynamic action during the reciprocation of the piston.
Further, it is disclosed in UK patent specification No. 21,62,614 that the plastic inserts are secured within recesses formed in the outer surfaces of the skirts, for example, by the inserts each being held in the co-operating recess, possibly each recess being formed with undercut portions, and the insert being formed with tongues each of a shape to be held within the associated undercut portion.
It is an object of the present invention to provide a piston having a skirt of a novel and advantageous construction.